A variety of automated guidance vehicles (AGV) have been developed, with a principal use of performing delivery or work functions in an office or industrial facility. The basic types of guidance systems used on these unmanned industrial vehicles have been permanent tracks, buried wire, reflected light, and radio controlled.
Track-guided vehicles ride along a fixed rail or a track and are guided by the contour of the track. This technique is often unacceptable, especially in office situations, since the presence of a fixed or permanent track on many floor surfaces is aesthetically, as well as physically, undesirable. The installation of such a permanent track is expensive; and it is diffcult and expensive to change the location of the track, thereby greatly reducing the flexibility of the system.
Buried wire guidance systems have been applied successfully to various material handling systems, including hospital food tray delivering vehicles and office mail carts. In this system, a wire is buried in the floor along the track the vehicle is to follow and both ends of the wire are terminated at an excitation source. This technique has serious limitations, including the impracticality of installing a buried wire system in an existing structure and the system's lack of flexibility.
In reflected light sensing systems, a brightly visible line, contrasting markedly with the surface of the floor, is laid along the path to be followed by the AGV. In this type of guidance system, there is no variation in the frequency of the incident and reflected light. The vehicle includes a visible light source that illuminates the floor and photocell sensors that detect the level of light reflected from the floor. Both the background and guideline illumination are detected to determine guideline position, but problems have been encountered with such reflected light sensing systems since spurious illumination from the floor has impaired the ability of the system to detect the difference between the guideline and the background illumination. Therefore, accurate tracking with a light sensing system may be unreliable, leading the AGV to follow a false, non-existant guide path.
A positive attribute of a reflected light system is that an existing line can be removed and a new guidepath applied. However, the impermanence and visibility of a guidepath can also be a drawback, since visible, removable guidepaths invite vandalism and are aesthetically unappealing. This aesthetic unacceptability often precludes the use of a visible light-reflected system in many applications. Another disadvantage of reflected visible light-tracking systems is they are effectively limited to use on flat hard- or resilient-type surfaces, such as concrete or tile. Problems with obtaining the necessary reflectance levels, and with the aesthetic undesirability of a solid, bright line on a carpet, prevents the application of such a guidepath on fibrous surfaces.
To overcome some of the above-mentioned disadvantages, automated guidance vehicles were developed that followed invisible fluorescent guidepaths. The guidance system of these AGVs works on the principle of applying a fluorescent dye-containing guidepath. As the AGV traverses the guidepath, a source of ultraviolet light on the AGV illuminates the guidepath causing the fluorescent dye to emit visible radiation, which is detected by photocell sensors on the AGV, and, through the correct circuitry, the AGV is steered along the guidepath. Generally, the photocell sensors sense the emitted visible radiation and produce an error output signal proportional to the variation of the vehicle's position from a predetermined lateral position with respect to the guideline. A steering mechanism then reacts in response to the error signal so as to correct the vehicle's position and to keep it on the guideline.
Although fluorescent guidepaths have been used to guide AGVs for mail delivery or material handling purposes, there are still several disadvantages. For use in mail delivery, these guidepaths are restricted in performance by the aesthetics of the office environment. In general, a guidepath must be virtually invisible when viewed under ambient office conditions, should adhere to a variety of substrates, must withstand normal traffic and maintenance, and should be easily deactivated to allow modification of the mail delivery route in case of office modification. An exception to these restrictions occurs in some offices, where a visible guidepath is desired to keep carts and boxes off of the guidepath.
In addition, the guidepath is necessarily designed to be detected by the AGV in a reliable fashion with a minimum of interference by other floor surface factors. For use with the present stimulated emission AGVs on the market, the guidepath must fluoresce in the visible range when stimulated by ultraviolet radiation. The guidepath must overcome potential interferences with changes in surface color due to bold patterns or transitions from one surface or surface area to another.
Numerous compositions have been used to apply a fluorescent guidepath. These compositions fall into two broad categories, solvent-borne solutions and water-borne emulsions.
The solvent-borne guidepath compositions previously developed suffer from a number of disadvantages. These formulations generally contain flammable solvents, requiring precautions to be taken during production, storage, shipping, and application. The solvent vapors liberated during application to a floor have an objectionable odor, requiring work to be performed after normal working hours. In addition, the solvents are toxic by inhalation, requiring full building ventilation and respirators to protect the workers during application.
The solvent solution formulations provide good visual aesthetics, acceptable traffic and maintenance resistance, and easy deactivation when applied to hard or resilient surfaces, such as composition tiles, marble, concrete, and ceramic tile. In addition, certain solvent formulations can be successfully used on most carpeted surfaces. Major performance failures of these systems include soiling of the guidepath after extended periods if proper floor cleaning is not maintained and a compromise in visual aesthetics, in many cases, after deactivation. In addition, the products used for deactivation of these guidepaths are flammable materials which liberate solvents during application.
The water-borne emulsion guidepath compositions previously used contained polymers which cure at room temperature upon mixing with a cross-linking agent. Mixing must occur immediately prior to application. The amount of cross-linking agent is critical to the performance of these coatings, requiring an involved packaging procedure. In addition, mixing reduces the useful life of the product from up to 12 months to only 24 hours, resulting in wasted product during field application.
The water-borne emulsion compositions provide acceptable visual aesthetics, outstanding traffic and maintenance resistance on hard or resilient surfaces, such as composition tiles, concrete, marble, and ceramic tile and can be removed with some difficulty using suitable solvents. On most carpeted surfaces, however, they produce visible guidepaths which cannot be removed. Thus, their practical utility is limited to hard or resilient surface guidepaths.
The present invention provides water-borne guidepath compositions capable of being applied to a variety of substrates without the need for engineering controls on respirable air. The composition includes an ionically cross-linked ionomer, eliminating the need for separate packaging of a cross-linking agent and mixing on-site. In addition, these ionically cross-linked binder compositions give good visual aesthetics, good traffic and maintenance resistance, and outstanding deactivation when applied to hard or resilient floors and to most carpeted surfaces. The compounds and compositions used for deactivating these guidepaths are non-flammable, do not release harmful solvents, and do not result in a compromise in visual aesthetics after deactivation.
In accordance with the present invention, a single-package guidepath composition, providing new and unexpected characteristics of guidepath durability, reliability and deactivation is achieved, which heretofore has been unknown in the art. More specifically, the coating composition of the present invention can be easily applied to several types of substrates, including hard, resilient and fibrous substrates, and after drying, provide an invisible coating suitable for guiding stimulated-emission controlled AGVs. The described composition produces a very durable coating that maintains the integrity of the guidepaths for long periods, yet the coating also possesses the novel characteristic of easy removal, thus allowing ease of variation of the guidepath.